1. Field of the Invention
The invention relates to a photographic telephoto lens system and, more particularly, to a compact high-performance telephoto lens system that has an aperture ratio of approximately 1:4 to 1:4.5, a half viewing angle of approximately 2 to 3.degree. and a telephoto ratio of approximately 0.8.
2. Description of the Prior Art
Lens focusing is normally carried out by moving the entire lens system. However, where telephoto lens systems are employed, an internal focusing mechanism is widely used in view of the fact that the degree of movement of the center of gravity is small, and to improve the ease of handling; see, for example, JP-A-No. 58-82217 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-No. 60-418 and JP-No. 62-24209).
As a result of the increased use of autofocusing mechanisms in cameras, the need has arisen to employ a simpler focusing lens group in order to reduce the load on the lens drive unit and thereby increase the focusing speed. However, conventional lens systems for auto-focus cameras have had various problems such as a bulky and heavy focusing lens group, a bulky overall lens system, and a complicated focusing mechanism.